Hello--I understand that you need at least 600x to view bacteria and some say 1500+ so 40x doesn't seem to be in the right mag. area at all--not sure this helps much.You could purchase a 100x obj. and 10/15x eyepieces but will probably be into oil immersion for the obj.Possibly a 20x eyepiece + a 60x obj will give you a degree of definition.I use a SEBEN Bino with this combi and it gives a small view but not good.kind regards martin r

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The oil goes between the cover slip of the slide and the objective tip. It can also help to put some between the condenser lens and the bottom of the slide. Be careful when using oil, as when rotating to lower magnifications, it is very possible for the 40x to get oil on it. The 100x is sealed to protect it, but the 40x is not. If oil gets on the 40x, it can seep up inside and destroy the lens.

It is also a very good practice to clean both the 100x and 40x after each use. If the oil sits on even the sealed 100x objective for any long extent of time, it will start to break down the silicon seal, and you can potentially have the same problem as with the 40x, where the objective acts like a wick of a candle and sucks up the oil, thereby destroying the objective.

Since you need to use oil at 100x, there is probably a good chance that there is oil on both the 100x and 40x objective. I see this a lot in my work. Since the working distance of the 40x is so close to the slide, what often times will happen is that it will accidentally get dragged through the oil while rotating to lower magnifications. The 100x is sealed to protect it against the oil, but the 40x is not, and if the oil sits on the objective for any length of time, the objective will act like a wick of a candle and **** the oil up inside of it. At that point it is more economical to buy a new object. The same thing can happen with the 100x, but it takes much longer for it to happen. Basically the seal around the objective tip is just latex chalking, and the oil will break it down over time, thereby causing the same affect as with the 40x.

You can try to clean them. If you are lucky the oil is only on the outside surface of the objective. Try using a que-tip and isophrapoyl alcohol to clean it off.

You can send the lens to Delta Optical Instruments, Inc.They can determine if your EF Plan 40x objective lens is repairable.The will give you an estimate prior to work or suggest a replacement if it cannot be repaired.email them at: robin@deltaoi.com

First, a scope of this grade will not be completely in focus as you move from one magnification to the next. But it should be close enough that you do not loose your point of interest.
Be sure you are not pressing down on the stage specimen platform as you change magnifications. It is very sensitive to pressure.
Also, be sure that the coarse focus tension is tight enough that the platform is not drifting down imperceptibly as switch magnifications. Look through the scope and watch if the image goes out of focus while you are watching it. If so, you have what is called "stage drift".
This is corrected by tightening the tension on the coarse focus knob.
The tension adjustment is on the coase focus shaft. It looks like a chrome ring with about 3 holes in it. There should have been a strange looking tool that came with your scope. It is used to adjust the tension. If your specimen is "drifting" out of focus, simply tighten the tension ring a little bit at a time until the specimen no longer goes out of focus. Do not get it so tight that it is not easy to operate the coarse focus knob.

For the red colour partical your illumination angle should be 0 degree.
As per you exepirience you are getting red at low magnification and not getting at high magnification. at the higer magnification the light deviation you can apriciate more then lower.

try to adjust your light source focusing lenc at higher magnification so at the lower it will be more better,

Seing bacteria isn't just about magnification, many
are transparent and need to be stained. Even at X1000, you will see little detail, but can make approximations of shape etc. Here is a good starting point for staining bacteria.
With a toothpick scrape a little plaque from your teeth (size of a pinhead is plenty). Put this in the centre of a slide with 1 drop of water and mix thoroughly. Allow this to dry then pass the sample through a flame three or four times (hot, but not hot enough to burn fingers) Stain for five mins using either Methylene Blue or Eosin. If you don’t have these, Blue or Red fountain pen ink will do for starters. Rinse off excess stain with very slow running water. Blot dry and observe at X400. If you have an oil immersion lens, you must use a cover slip and mount your specimen in balsam first.
If I can be of any further help, please don’t hesitate to ask.
Cheers…..Dave